I've just bought a house with a 7,000L outdoor swim spa (about 1800 gal for you guys across the Pacific)
It was filled up and had been running before we moved in, except that it was shut down for two weeks because the heater element failed and they/we were waiting for a replacement). It runs of a SWG.
The element was replaced the other day, we've brought it up to temp, and I brought a test kit.
The chlorine test (DPD) goes clear as soon as the tablet starts to dissolve (a slight pink during the dissolving) which from what I read previously can be due to high chlorine. The local pool store tested with the same result.
As my wife is keen to get in, I bought some Sodium thiosulphate to bring the levels down and turned off the swg. I've added 300g in stages, which by the calculation on the pack should drop the level by 42ppm. It still bleaches out the test.
If I dilute it down to about 1/5 with tap water, it reads around 5 (max on the test chart).
There are also some pool-check test strips the previous owner left that I believe are a tetramethylbenzidine test. It should go from clear to a dark blue. It goes a dark brown, which I assume means it's still way over.
There's not a lot of sunlight at this time of year and it's pretty cold.
What's the best option?
Leave the cover off throug the day?
Run the blower to aerate it and drive more Cl out?
More sodium thiosulphate?